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What is the meaning of first flight and introduction in aircraft production?

They are info from wikipedia (here and here). I don't know many about the B-52 Stratofortress, but I'll take another case. The N-250 I remember its first flight which was performed with large scale, watched by Indonesian's former President and many other high rank officers. I remember the date, or at least the exact year. It was 1995.
Then my question is, if 10-Aug-1995 was its first flight which was performed with great fully, then what is the meaning of introduction (15 June 1997 in this case)?. If it was widely open to public when performing first flight, then why does an airplane needed to be introduced?

The first flight of a new aircraft type refers to the first time the aircraft is flying during the development and testing phase. If the testing goes smoothly, it might be that no more changes are necessary and the aircraft can be delivered to customers as it is. But if problems show up during these test flights, changes might be necessary before finishing the final design.
The introduction refers to the first flight by a customer (an airline for commercial airliners or a military unit for military aircraft). This is also referred to as entering service. This could happen in the same year as the first flight (e.g. Boeing 737 Classic series in 1984) or many years later (e.g. Concorde in 1976, 7 years after the first flight in 1969).
Another term commonly used is the launch of an aircraft type, which refers to the start of the development program.

The IPTN N-250 you mentioned was never introduced into service. Wikipedia claims the 15 June 1997 as introduction date, but on this day the aircraft was shown at the Paris Air Show:

(image source: airliners.net, taken by Peter Vercruijsse in Paris - Le Bourget on June 15, 1997)
The image description says:

"Gatotkoco", the prototype N-250 returning from a demonstration flight at the Paris Air Show. The N-250 programme is currently (early 2000) on hold due to a lack of finance.

This does not count as introduction and is therefore a mistake in the Wikipedia article.

I'm a bit confused with the delivery process. Are you talking of the first ferry flight, the last acceptance flight, or the first commercial flight?

@ManuH these would probably all occur very close to each other, but introduction should generally refer to the first commercial flight. I clarified the answer.

As I took the case, the N-250 of Indonesia, the status is canceled. Mean, no one was delivered to any customer. So, never be any entering service, however.

Quote: This does not count as introduction and is therefore a mistake in the Wikipedia article. That make sense. That airplane is just parked now in the manufacturer hangar.

Between those two events are 2 major steps:

Flight testing by the company that builds the aircraft. This is a series of test flights in which the aircraft is tested under all circumstances it will be expected to operate in.

The first few flights are just to make sure all the aircraft systems work as expected in flight
Then there are flights to explore the performance envelope (flying at different altitudes and speeds), this is done in incremental steps (slowly increasing flight speeds, G-loads etc.).
Then there are environmental tests (flying in cold/hot weather)

When the test flights are concluded to satisfaction, and any modifications have been tested as well, it's time for certification: basically, another series of test flights, this time they are monitored by the certification agency. They also dictate which tests have to be done.

First flight may be a public event, but the aircraft is far from ready for commercial use. First flight is a PR exercise, with the company showing their new project in a working state for the first time.

What about introduction? In the case N-250, it was canceled when it ready for certification. Please read Wikipedia here if you are interested.

The Wikipedia article is incorrect. N-250 was never certified, so it never flew commercially. Maybe the introduction was planned to be in 1997.

That make sense. Now I understand what mean "introduction."

Of course it is rather difficult to "hide" a complete airfield and prevent every member of the public from seeing an aircraft take off and land, but a first flight is not necessarily organized as a public event. Often, it just happens as soon all the pre-flight ground testing has been completed, and the weather is suitable. In fact there is nothing much to see - a first flight is not going to be a quick low level circuit around the airfield. Unless there are serious problems, it is likely to last for several hours, while all the aircraft systems are checked out before the first landing.

Typically, introduction means introduction into service. For passenger aircraft this means the first delivery to the customer and/or first revenue flight.
For military aircraft this means the first date that an aircraft is declared operationally ready to perform (part of) the intended tasks.
This usually occurs some time after the first flight because the test program has to be concluded. Depending on whether it is  a modification of an earlier certified model or a totally new aircraft, the time between first flight and introduction into service can range from several months to several years.

Typically, introduction means introduction into service. For passenger aircraft this means the first delivery to the customer and/or first revenue flight, as I showed, the N-250 of Indonesia was never delivered to service was I was canceled. So, how it introduced? You may read the Wikipedia for detail.

@AirCraftLover: Well, obviously, the Wikipedia editor who added that information uses a different definition of "introduction" than you do. If you want to know what precise definition they use, and why, you will have to ask them. On April, 25th 2013, an anonymous user added "Introduction: 1996" to the article, on April, 27th, it was changed to "1989", on June, 21st to 1986, …

… on July, 12th it was removed again, on April, 11th 2014, it was set to "15 June 1997" by user Yoshiharu10. So, this is the person who can really tell you why they wrote on the Wikipedia article that the introduction was in 1997.

Thank you Jorg for your detail checked. As explained by Bianfable above, I believe the airplane is never introduced as it was never went even to certification. So, the best is to consider that the info on Wikipedia was invalid. The N250 itself is parks in the manufacturer hangar until today. Mean, never went to service.


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How many tendencies are affected by Gyroscopic precession for single propeller airplane?

I have heard about LEFT turning tendency affected by gyroscopic precession of propeller (which is turning clockwise or counter clockwise if seen from front side). But I just watched a video on Youtube explains the tendencies affected by the gyroscopic precession, that the airplane is pitch up (nose up or tail down), which means, there are two tendencies.
Then my question is, is that explanation true? Is the second tendency true?

Both are wrong. (Or rather, both are partly right, which makes them fundamentally wrong).
Precession happens when there is an 'input' rotation (moment) and not by itself. When you balance the airplane to fly straight and level, there is no gyroscopic moment.
The gyroscopic moment is perpendicular to the external rotation, so it can be directed anywhere across the spin axis.
On a typical airplane with the CCW prop (or turbine for that matter), if you yaw (or turn) LEFT, the airplane will want to pitch UP. (See the diagram on your picture). If you pitch UP, the airplane wants to turn RIGHT. If you pitch DOWN, the airplane wants to turn LEFT.1 And so on. The quicker you maneuver, the stronger the effect is. (And of course, the quicker and heavier the prop is, the stronger the moment, so it's most noticeable at full power).
In normal flying with GA airplanes, the gyroscopic moments are rather minor. The typical 'left turning tendency' is caused by aerodynamics. Gyroscopic moments manifest themselves when rotation is relatively fast, e.g. in aerobatics or spin. But they can be observed with quick impulse inputs on the pedals or yoke, if carefully executed.

1This latter is particularly noticeable on taildraggers during takeoff when the tail is lifted too quickly: the aerodynamic forces are still weak, and the power is full.

It's most noticeable on a taildragger if you raise the tail from 3 point to tail high very quickly while taking off.  If it has a large prop at TO power the swing to the left is quite dramatic.

An excellent demonstration of this principle is to remove the front wheel of a bicycle, hold the axle, and have someone spin it up for you.  Now, try to move the axle one direction or another.  You will see and feel the movement taking affect 90 degrees off from your input.

Good answer. Would be more precise if you reword the first paragraph to state gyroscopic effect is only present if the aircraft itself is undergoing rotation.

Doesn't the 2rd paragraph (and all further text) state exactly that?

@JohnK, thanks, I added this example to the answer.

@Zeus, to make the same understanding, I assume that we have the same understanding that CCW is seen from front side as in the picture, which actually it is clockwise or CW seen from tail side, which is the correct point of view.

I have to be very careful to read your explanation. So I will break it to some part to make sure that I understand it correctly.

(On a typical airplane with the CCW propeller): This one: If you pitch UP, the airplane wants to turn RIGHT, and this one: If you pitch DOWN, the airplane wants to turn LEFT. -->>I understand. But this one: If you yaw (or turn) LEFT, the airplane will want to pitch UP. -->>This is I don't understand. it relevancy probably, If I yaw (or turn) RIGHT, the airplane will turn pitch down.

I tried to search about gyroscopic precession, and I found interesting thing here, start from 23:00, the turning is proportional to its lean. When he LEAN to RIGHT, it TURN RIGHT. Vice versa, when he LEAN to LEFT, it TURN LEFT. I assuming the bicycle's whee; is the propeller and his left hand is front side of the propeller and his right hand is airplane's body. So, pitch UP is like LEAN to RIGHT which will TURN RIGHT and pitch DOWN is like LEAN to LEFT which will TURN LEFT. Am I right?

Traditionally, prop direction is defined when viewed from the front: this is how you approach it and how you turn it when starting by hand. Most examples assume (often without stating it) CCW rotation because it's by far the most common on American airplanes. But I agree strictly speaking it needs explicit qualification.

As for direction, it is always 90° to the applied moment. (Direction of any moment can be defined by the right hand or right screw rule: it goes along the screw when you turn it by the moment in question). Precession is a cross product of the spin and external moments; check the cross product definition to understand its direction. Precession is proportional to the applied moment but not to the angle ('lean'): the stronger your external moment (i.e. the quicker you turn), the stronger the tendency to turn crosswise. ('Turn' here is any rotation across the spin axis, i.e. pitch and yaw).

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Why do the B747 of NASA Shuttle Carrier Aircrafts (SCAs) need additional vertical stabilizer?
Here is picture of B747 SCA of NASA and the AN-225 SCA. There are additional vertical stabilizer in the tip of the elevator to the Boeing's, while the AN-225 is designed with the vertical stabilizer located at the tip of the elevator. As we know, AN-225 was also designed and intended to carry Soviet's Aircraft. Then my question, why do the B747 of NASA Shuttle Carrier Aircrafts (SCAs) need additional vertical stabilizer?

Here is an excellent podcast which talks about the SCA, and the guest is a pilot who flew SCAs for several years: https://omegataupodcast.net/195-flying-the-shuttle-carrier-aircraft/. I definitely recall they talked about the modifications that were required to the 747 to carry the shuttle.

The AN-225 was designed primarily for carrying the Buran, so they didn't have to make structural changes to an existing design to accomodate the carrying of the shuttle. The aircraft was purpose built for that mission (although it never really saw much of that in practice).
The NASA 747 on the other hand, is a stock 747 that they added the ability to carry the Space Shuttle on its back. They couldn't remove the vertical stabilizer on the 747. Due to the shielding effect of the airflow when the shuttle is attached, they needed additional yaw control that required them to add the outer stabilizers.
The 747's used by NASA were converted passenger aircraft. The first one, N905NA was acquired from American Airlines made in 1974, the second one N911NA was bought from Japan Airlines, built in 1973 and acquired by NASA in 1990 or 1991.

Can you please what is this meaning? Due to the shielding effect of the airflow when the shuttle is attached, they needed additional yaw control that required them to add the outer stabilizers. What is that mean the shielding effect?

There is a big wall (the orbiter) in front of the stabilizer. As air flows around the shuttle, it shields (or blocks) some of the airflow around the stabilizer making it less effective.

Thank you my friend.

There is an additional, possibly bigger reason than blanking of the tail by the shuttle.  It's the same reason finlets and ventral fins are added to seaplanes.  The side area of the shuttle ahead of the vertical aerodynamic center of the mothership is significant, and has the effect of reducing the weathervaning ability of the 747's vertical tail (imagine making the front arrowhead part of roof top weathervane larger; its weathervaning tendency is reduced).
Float planes have the same problem because most of the side area of the floats is forward due to the profile of the float's hull.  I've flown float planes that didn't require additional fin area aft when floats were installed, but should have.  You really notice the reduction in yaw stability.

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What happened to the power plants after an aircraft is retired?
Few weeks ago, there was a Boeing 747 belong to an airliner retired in our country. I am not sure what series is that, but seems it is 747-200. What then will happen immediately to the power plants after it decided to be retired? Is the power plants will be reused, at least for another purpose?

Related

Also: Jet engines: are they owned by the airline or just rented?

They'll go on another airplane, or go into inventory as spares, or maybe go for overhaul if they are becoming or close to becoming worn out (the can be run until the Inter Turbine Temperature at takeoff or oil consumption becomes excessive, or they fail an internal inspection, or suffer excessive vibration etc).  Engines are changed all the time, every few years, and can be thought of as a separate asset from the individual aircraft.

Thank you John. That was on my though, too.


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What is the official unit of airplane/aviation speed?
Some units I read/found are commonly used in aviation: mach, knot (nautical mile per hour), mile per hour (mph), kilometer per hour (km/h or kph).
"Official" meaning like the units used by the flight data recorders, if a pilot makes a report of their speed, and so on.

Related, maybe a dupe?

Knot. Pilots think and communicate with ground personnel in knots. HUD tells you knots. Textbook tells you to increase speed to 500 knots after takeoff, and land at 150 knots.

You might want to add a US in front of Pilots, Textbooks and Instruments.

As said above, Knots are used internationally mainly for convenience. 1 Knot =1 Nautical Mile/per hour. And a Nautical mile is 1 degree taken at a meridian i.e a great circle.
This relation comes quite handy for navigation since if you traveled at 1 kt you’ve done 1’ of arc in 1 hour....

So, the distance of nautical mile will be different between equator and near the polar, right?

As usual it calls for a Well, But... answer.
The legal unit is worldwide km/h, kilometer per hour.
For all practical purpose most countries use knots, except when it comes to high altitude flight, when the mach number may be used in reporting.

"The legal unit is worldwide km/h": Which law are you referring to?

The law of nature :)) But serious, Measurement is worldwide defined in SI units. Satute and nautical mile are since quite some time no longer based on their own definitions, but defined based on the meter. Practical usage of miles and thus knots is therefore legally use of km (and km/h).

As far as I understand, ICAO is the international body for recommendations in international aviation. Then each country writes an AIP where it states any deviation from ICAO recommendations. Regarding units, this is part of Chicago Conv. Annex 5 which states that there is no date to stop using foot or nautical mile or knot. Only China and Russia have switched to SI units if I remember correctly.

@mins Mind to read my reply at whole? Even the mile is nowadays defined by using SI units. it's no longer a defined as a latitude minute, but 1852m. Isn't it? Thus the legal base is the meter. And That's as well why I diferentiated between legal definition and practical use - much like ICAO does.

"Mind to read my reply at whole?". Your explanation says: 1/ The international legal unit is km/h, 2/ Most countries use an illegal unit for practical purposes. More correctly: 1/ There is no legal unit worldwide, 2/ There are 2 sets of recommended units at ICAO level, including knot. 3/ ICAO units are made legal in each country via their AIP at paragraph GEN 1.7, except for China and Russia if I recall well (unfortunately their AIP is in restricted access). US never completed its national switch to SI units.

@mins Sorry, but you're implying something that neither has been said, not is true. More specific it's you point 2 by assuming there is an illegal unit. Or in your notation: 1/ The legal unit for length, worldwide, is the meter. 2/ The nautical mile is an alternative name for a 1854 meter, not a genuine one like the meter (not even a  derivated unit).  3/ ICAO allows the temporary use of such alternatives for practical purpose 4/ This does not even touch the fact that the only legal unit is the meter.

"ICAO allows the temporary use"... well, ICAO documents are recommendations, they can't allow or deny anything, each country is sovereign. Country AIP is the legal document, and unless the knot unit is refuted in paragraph GEN 1.7, its use is legal in the country, for international  aviation purposes. Do you have an AIP, e.g. for the US (where the knot is even a civil legal unit) which states the ICAO alternative set of units is illegal? If not, then knot is legal, per ICAO recommendation enforced by AIP.

@mins Lets cut this short, may I ask you to look up the actual definition of a nautical mile and then reevaluate this issue?

@mins, just to nitpick: China and Russia never 'switched' to SI units (in aviation), they always used them. (Continental) Europe did too, but switched to knots/feet after WWII due to US/British influence.

@Zeus: I didn't know, good addition.


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What is this part in Embraer Legacy 650 and what is it function?

The picture I took from here. If you want to see, just click the link, it will take you to the part I want to show and ask. What I want to know is its name and its function.

Closely related, maybe a dupe?

They are called strakes, they are available on lots of airframes and help cut down on dutch roll and increase vertical stability.
Here is a nice overview of the strakes on a king air with lots of cool diagrams on how they work.
For the Embraer Legacy they also can negate the need for a yaw damper on MEL lists which can help increase dispatch reliability:

Strakes have been added beneath the rear fuselage and vortillons
beneath the leading edge of the wings to increase stability,
especially because of the yaw produced by the winglets. Although the
ventral strakes do detract somewhat from the aircraft’s clean lines,
they make up for it in dispatch reliability, since the strakes can
negate the need for a yaw damper on the MEL list for short periods.
The strakes under the leading edges of the wings assist with air flow
over the ailerons.

MEL = Minimum Equipment List. If one item on the MEL isn't working, the plane cannot legally fly.

@PeterKämpf Weirdly, in practice the MEL is exactly the reverse. The document tells you what you CAN have inoperative in order to dispatch, and what limitations (i.e. no ETOPS with an inoperative APU, in the 737), if any, apply.  Any item NOT listed in the MEL can not be deferred. For instance, nothing in the MEL states that "both engines must be operative," but since nothing in the document allows dispatch with an engine inop, they're both required. Ditto all hydraulic systems on the 737, all 5 hydraulic pumps, etc. Yeah, it's not at all what "minimum equipment list" means in plain English!

That said, Dave's point is correct that having the strakes means that the Y/D can be deferred for some length of time.  Absent the strakes, it would be required for dispatch.

Thank you for your explanation.


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Why is this angle of attack sensor tab not symmetrical between the leading and trailing edges?

Here is an Angle of Attack (AoA) sensor I took from here. If you are interested to know the AoA detail, just click the link. You may see what is inside it. But not sure what airplane's AoA sensor it was, he didn't mentioned it, but he said from Soviets' airplane. And my question is, why is the trailing edge is not smooth and gradually reduce the tip, not just like wings trailing edge? I mean, in the trailing edge there will be curl or eddy's current. Why didn't it make symmetrical between the leading edge and its trailing edge so it will smoothly release the air?

It's probably more accurate that way, and the drag penalty is trivial.  But as to why it is more accurate that way-- ??

The shape seems to be a combination of a wedge and a parachute, which would adjust rapidly to a change in airflow and have structural strength.
A cone has 10 times more drag than an airfoil, and, importantly, a sharp leading edge that will respond instantly to a change in airflow.
The wedge/drag combination minimizes reading lag from inertial acceleration, allowing for heavier and stronger construction.  It looks like a meat cleaver, and will likely last as long too.  This would be an important consideration flying through frozen precipitation, such as hail.
A slight "boat tailing" or rounding of the trailing edge, along with the mass of the vane, would render reading fluctuations from trailing edge turbulence much less than the "steering" effect of drag and the leading edge "wedge".  In short, the design is rugged and reliably works.

Notice where the "pivot point" is compared with the US Patent 5,438,865


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What is this object in the cockpit of an ultralight?
This is a tool (probably) in on an ultralight airplane. Initially I guessed that it is a tilting meter (to level between right and left), but seems it is not as it just a vertical tube filled up with something like liquid.
So, what is that and how does it work?

It's an airspeed indicator for ultralights.  The pitot inlet is at the bottom and the pitot air pushes a little red plastic disc up and down on a central rod, with a calibrated clearance between the edge of the disc and the walls of the tube.  They are very sensitive and are good down to 10 MPH or less.  You'll also see them on hang gliders.
See here:
https://www.aircraftspruce.com/catalog/inpages/hallwindmeter.php?clickkey=5468

Remarkably similar in construction to an instrument that anesthesiologists use to tortu^W measure the lung capacity of post-operative patients.

It's indeed an airspeed indicator.  Here's one at Oshkosh 2018, with me blowing about 27 knots into it.

I don't see an ASI in the panel.  I am unable to confirm this guess, but it could be an airspeed indicator (ASI).  Google Dwyer Wind Speed Indicator.  The Dwyer is plastic, wider at the bottom, and works by having the wind push a ball up a tube that gets progressively wider near the top.  As the airflow pushes the ball up, more air can leak around the ball.  Where the ball reaches equilibrium indicates the speed.
Edit: @John K beat me to it!  Thanks, John!

The Dwyer is plastic, wider at the bottom, Isn't it wider at the top?

Yes.  My bad.  Dwyer is wider at the top.  Sorry!


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Does a converted aircraft require recertification? Does it break manufacturer rights?
Here is a very interesting video shows how an Airbus A330 is converted from passenger plane to a cargo plane. There are lots of changes or modifications were made to the airplane to fit the new requirement as a cargo airplane, including removing the passenger seats, strengthening the floors, change the windows and the doors, and many more.
So, what I want to know are:

Is such that changes require recertification?
Is that conversion is not breached manufacturer right which there is stated that only the manufacturer can do repairing, modification, and so on?

As for 2. if the client has not purchased the plane with a specific maintenance plan, the manufacturer has pretty much no say in whatever the owner wants to do with the plane. The manufacturers type rating for the plane will, of course, become void if anything major is done to the plane.

#2 is a grammatical mess.  What is the actual question?  Are you saying that the manufacturer DOES have exclusive rights to perform repair and modifications, or asking whether or not they do?  (Because if they do, such a mod would obviously breach this clause, and if they don't, it wouldn't... )

At this point in the video it says about a the verification of
all the modifications done to a plane would be verified by an independent third party.
Similarly in this website from Stirling Dynamics, I could find:

Any changes to the original aircraft require a detailed analysis of
the proposed changes and the presentation of design evidence to the
applicable certification authorities for airworthiness clearance.
The certification basis for this programme has been agreed with the
FAA under a Supplemental Type Certificate (STC) and will also be
validated by the European Aviation Safety Agency (EASA) and the
Civil Aviation Administration of China (CAAC).

So, A330 and A321, and it is clearly that the modification of the A321 requires recertification of FAA, EASA, CAAC. It is said under the Supplemental Type Certification (STC). So I think, the modification/conversion of the A330 is the same requirement with the A321, it is requires recertification from at least from those three agencies.  So, I may accept your answer as the answering my question.

@AirCraftLover Note that an STC is not a complete recertification. It is (as the name suggests) only supplementing the existing certification.

Generally no the aircraft will not need to be re-certified however the aircraft will likely need an updated weight and balance.
Aircraft have their official weight and balance numbers measured as they are currently configured. If an airframe has its interior pulled out and some reinforcement done to the airframe it will need a new weight and balance drawn up. This is true for all aircraft from pulling the back seats out of my Cherokee to stripping out a 747 for cargo work.
In terms of the modification, pulling interiors generally does not require getting the manufacturer involved, many service/repair facilities are capable of this job. There are even third party doors that can be used for the modification which carry full certifications (STC).
Some cargo outfitting may also change the way the aircraft is flown as well…

The comment of @jcbge below regarding the A321 is almost the same case, so I think it is clear that require recertification.

@AirCraft Lover, I think you may be mixing the terms "inspection" with "recertification".  The types of modifications you describe aren't generally done without approval, instead the configuration is preapproved, or certified by an authority.  Once the work is complete it must be inspected to ensure that it conforms to the TC or STC.  I wouldn't necessarily call the inspection process "recertification", but I have heard the it used this way.  (I have also seen "conform" and "conformity" used when the actual action performed is an inspection...)  Not saying you are wrong, just clarifying FWIW.

@MichaelHall, according to the link provided by jcbge above, there is mentioned that "Any changes to the original aircraft require a detailed analysis of the proposed changes and the presentation of design evidence to the applicable certification authorities for airworthiness clearance". So, it is required recertification. Of course, different level, just recertify those changes.

@AirCraft Lover, yes, I agree that a configuration change (for the first time) requires certification and a supplemental type certificate.  My point is that subsequent conversions to an already approved STC just need to be inspected to ensure that they comply to the specs.  And that some people may refer to this as "re-certification", but it is really more accurately described as a conformity inspection.

As far as I know，conversion programmes can be in the TC or in the STC
if you search for 737TCDS on faa.gov , you can see 737BCF in that document.that means Boeing has a original 737-800 cargo conversion program
other choice is throught STC, third-party stc holders as AEI ,IAI are also certificated to convert 737-800 from passenger to freighter, as for your question 2,I'm sure AEI and IAI have paid Boeing money for stastic support

Please edit your answer to usesentences and proper punctuation.  As your answer is currently written, it is very hard to read.

It was Airbus A330.


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Why do shipping companies opt for the Boeing 747 instead of Antonov An-124?
Both are quad-jets, but the Antonovs can carry up to 150 t of payload and are much cheaper (\$100M for the An-124 compared to \$238M for the Boeing 747-400F).
I understand that MRO is quite an issue for Antonov, but we are talking about the freighting industry, which is less congested and less demanding than the commercial airliner industry.
Is the skepticism of buying a SSSR-era product really founded, or is there in the West a lobbying trying to maintain the Airbus-Boeing duopoly and keeping foreign products out?

I think it's less about skepticism than it is about actual cost to use. Sure, the actual unit price at purchase time is lower, but the An-124 is way more scarce, and if it were to serve the same demand as the 74F, the per-use cost would be astronomical. I'm quite sure the per-use cost is already way higher for the 124 anyway. That's without getting into the comparatively nonstandard gate configuration.

Hm, I didn't think about that. But can you explain why you think that the cost per use of an An-124 would be actually higher if it served the same demand as the 747F? I didn't understand it quite well.

if it served the same demand -- it can't. There are so many fewer 124s than 74Fs that it's not reasonable to draw a comparison, and since the 124 is best suited for specialized, oversize loads, Volga-Dniepr likely understands that it's a niche product in a seller's market. They charge as much as customers are willing to pay within competitive boundaries.

Maybe this should be a separate question, but until that time: why "is [the freighting industry] less congested and less demanding than the commercial airliner industry"?

It's interesting to note that Volga-Dnepr, the largest civil operator of the An-124, also operates the 747-400F as well as the 747-8F.

@0xdd Now I get your point. This is exactly the core of my question. Why is the An-124 a niche product and hasn't gone mainstream? What stops them from expanding, yet the potential is there. Neither are recent design. As of the 747, their first serious freighter variant came from the 747-300 and was completed in  1983 while the An-124 was entirely designed as a cargo plane and entered service in 1986. They arguably entered into the freight transport at the same time, yet shipping companies have not adopted the 124s and now Boeing has a large advantage to a point where they don't compare. Why?

Don't think this is an "opinion based" question at all. It isn't asking for our opinions; it should be possible to provide an entirely objective answer.  That answer may discuss others' opinions, but "the 747 is widely perceived to be more reliable & sustainable" is an objective statement of fact. Even when that fact is about the perceptions -- a.k.a. opinions -- of industry decision-makers. "What's the best airliner" is opinion-based; this question is not. (imho)

why is it a niche product -> because most people don't need to transport oversize cargo like that. There are standard cargo containers that go on planes and the 124 is explicitly designed for stuff that doesn't fit on those. Packing stuff into those standard containers or even onto pallets is on average more efficient than transporting, say, an unboxed tank or helicopter, which is more up the 124's alley.

@Bram That was entirely opinion-based, but I think it is justifiable. Cargo planes spend more time on the ground. Passenger operations are rigourously scheduled whereas cargo is on demand. According to TomMcW here, passenger aircraft made about 6-8 flights per day whereas the FedEx planes were making 4-6. Therefore, from an MRO standpoint, cargo airliners are more tolerant, they can have a longer waiting time for a needed part; something passenger airliners cannot afford.

On the other hand, cargo revenues have been declining for a while now. And doing 4 to 6 versus 6 to 8 flights per day might give you a few extra hours to replace a part or fix something, but I'd be highly surprised to learn that makes a substantial difference in their reliability requirements. Operating lower-value aircraft, allowing one to maintain a larger fleet for the same capital investment (i.e., having extra spare aircraft), will have a larger impact on that.

@0xdd I admit it is undeniable that most people don't need to transport oversize cargo such as tanks or helicopters, but I must disagree with the rest of your argument. The An-124 is also convenient to carry pallets and can carry up to six 40-foot standard containers. Moreover, I don't believe there should be an upper-limit when it comes to payload-capacity  for cargo planes. If we look at the maritime transport where companies like Maersk and CMA CGM continuously build bigger container ships, I think more capable cargo planes will reduce the cost disparity between air and maritime transport.

There is an upper limit to aircraft size, see here, and it's substantially more stringent than in the maritime sector.

@billyandriam the upper limit is determined by the fact that most airports and logistics companies can't/won't handle oversize cargo, including loading IMCs onto a plane.

@BramThank you for noting these. I am getting off-topic from my original question but whatever. From my understanding, the limit is purely dictated by aerodynamics laws. Quoting Peter Kämpf "there is no clear boundary, and advances in materials help to shift the size limit up". Hopefully with time, thanks to better technology, we will see bigger than the An-225 plane.

@0xdd So actual airport infrastructure impose a limit when it comes to plane size, but this is an issue that the maritime sector has faced and is overcoming. Large cargo ships require larger container gantry and therefore, larger ships can only dock on the largest port, yet more and more ports are adapting to accommodate these new sea giants. The infrastructure should not dictate the design of a plane size, but instead play catch-up when more innovative and bigger cargo planes are built. Moreover, most of the time these planes only carry regular pallets or containers and not specialized cargo.

@0xdd: How do you load instrument meteorological conditions onto a plane?

This won’t be a real great answer, just major hurdles off the top of my head for wider AN-124 service.

Much shorter range. At 80,000 kg the AN-124 gets 4500 nm. 747-400 has a range of 7670 nm. 1
747 is slightly faster, cruising at .855 Mach
AN-124 is designed for a crew of 6; 747 has a crew of 3, or even 2 in the 747-8F
It would probably take Antonov a long time to catch up with Boeing’s production rates. 747-8’s are being produced about one a month. Back in the 70’s they were pumping out 80 or 90 of them per year.

I can’t find any numbers on fuel efficiency, but being that the Antonov was designed for military transport I would be very surprised if it could compete with the 747 in fuel usage.
1 I was not able to find good range numbers for the Antonov. It’s hard to really pin down the numbers on the 747 also due to the number of variants. The numbers here are taken from the Wikipedia page for each.

The 747-400 also has a crew of 2, just like the 747-8.

This makes sense. The shorter range and a manufacturing plant unable to satisfy a substantial high demand are definitely real technical hurdles.

I think the estimated range for the An-124 in the answer is too high (imho). If we were to trust Volga-Dnepr's Cargo Calulator, it says that loading cars onto the plane, making a payload of 90 t leaves us with a range 4600 km. Moreover, transporting a payload of 35 t gives us a range of 8600 km, which is roughly 4500 nm.

The An-124 is not available new: Antonov stopped production in 2014. There are plans to restart production by the end of 2019.
Existing aircraft are owned by the Russian air force and by a few specialized freight companies. Neither are likely to sell their aircraft. So the An-124 is not available.
If you really wanted to buy An-124s, you'd have to restart the production line. In the past, Antonov tried to sell an An-124 version with Western avionics and engines, but the development cost required for those modifications was too high to make this an attractive offer.
Among Western companies, Russian aircraft are not popular. See the absence of Russian airliners in Western fleets. Antonov's attempt at a Westernized An-124 was intended to address Western mistrust in Russian engines and avionics.
The operating cost of an An-124 is probably higher than that of a B-747 (due to less efficient engines).
The extra internal volume might come in handy (IIRC cargo flights are often volume-limited) more than the extra payload capacity, but you'd have to find a way to utilize that volume using standard containers. You don't want to repack all your cargo if it flies one leg of its route with an An-124.
Because much of the extra internal volume is in height, you might have to build a second floor, which complicates loading. And IDK if the cargo hold is high enough to fit 2 layers of containers.

You might want to check your sources about the collapse of Antonov. I believe that Antonov was taken over by state owned Ukroboronprom in 2015. No idea if they can still produce the An-124, but they do produce aircraft. https://ukroboronprom.com.ua/en/produktsiya-ta-poslugy/medium-transport-multipurpose-aircraft-an-178.html

I've amended my answer.

The Antonov 124 does not accept the standard ULDs and is very time-consuming to load and onload. While the did have some form of pallets in the early days these were very heavy and added to the non-revenue weight.
The 747 freighter on the other hand will accept common commercial pallets/containers or commonly called ULDs (unit load device) and this cuts down tremendously on the loading time as well as the transloading of cargo. A 74F can fly from Singapore to Dubai with a full load of 29 (30 for 744F) maindeck and 9 lower deck ULDS and these can be offloaded in Dubai and loaded onto another aircraft without dismantling. This cuts down the handling time.
The AN-124 does have an in-plane handling system but its just an overhead crane where pieces of freight have to be hooked up and drawn into the plane. Its not a user friendly system and thats why Antonovs usually have their own loading crews. The 747F OTOH has a well-designed in-plane loading system which enables quick loading and offloading with minimal training required. The systems are also common on all planes so anyone anywhere can load and unload the plane easily.
The low-purchase price is probably out of date and pretty meaningless. Go try and buy one and see. The supply chain for parts is also abysmal. If the aircraft breaks and a part is needed it can take days.
The forte of the AN-124 is in handling outsize/heavy cargo, the floor is suitably strengthened from the design stage to handle these items. The 747 was designed from the get go to only handle ULDs. The cargo floors on these aircraft are only designed to take the weight on the aircraft frames, the floor panels are just composite fillers for the most part and in in fact Boeing left them out completely in the lower-deck holds, leaving the only the frame structure to support the pallets and some small pathways for the loaders.


text:
Why does this Strikemaster have a textured leading edge?
I was at Duxford recently, and spotted a Jet Provost Strikemaster that had a rough texture applied to a portion of the leading edge of the wing.

Why was this applied?

Looks like part of the leading edge is missing and someone put in a rough patch awaiting the proper part, this is definitely not normal for any Strikemasters, and not for the Mk.80/80A in particular that were used by the Saudi air force.

My guess: cheap attempt at a vortex generator. See answers to this question for the purpose.

@DeltaLima: Almost - it's artificial roughness to trip a laminar boundary layer.

Have you considered emailing Duxford to ask them? They'll likely know a lot about their planes.

The leading edges are roughened to improve the stall characteristics. Typically vortex generators are used for this purpose nowadays.

The 5 and the 5a were used by the RAF for pilot training and the nose strakes were fitted to improve the spinning characteristics - the leading edges of the wings had a roughened paint finish to improve the stall characteristics. The 5s with the tip tanks (I'm not sure if 5b is an official or 'unofficial' designation) were used by the RAF for nav training and didn't have the nose strakes (not sure about the roughened wing leading edges) I don't know if it was because the tip tanks themselves improved spin handling or if it was because they weren't flown by studes for spin training.

(source: User "Fritag" at www.britmodeller.com)

The rough grey coating on the wing of the aircraft was applied in order to break up the smooth airflow and give an early indication of the onset of a stall as the T5's original clean wing design gave the pilot little prior warning.

source: all-aero.com / RAF Museum

A great deal of work has been put into stalling, spinning and
  stall-warning over the years of Jet Provost and Strikemaster
  development. This has led to all sorts of devices, like
  inverted-aerofoil tailplane, fences under intakes, strakes round the
  nose, roughened outboard leading-edges and little "eyebrow slats" at
  the wing roots. Of all these devices, the Strikemaster requires only
  the "eyebrow slats" to give it that precious smooth spin, a tidy g
  break in the stall and a distinct stall warning.

source: Flight International 12 October 1972 500-501

At first it was forecast that the T.5 would take the place of the T.4
  on certain roles such as high altitude training. Unfortunately the
  majority of T.4s had to be taken out of RAF service much earlier than
  anticipated so the T.5 had to take on more responsibilities. As a
  result, the RAF decided to update its fleet of Jet Provosts with new
  avionics suites, spin strakes, and roughened leading wing edges in
  1973.

source: Jet provost heaven

Not sure you should use dudes posting on an aeromodeler forum as source data. Just sayin'...

@JohnK If you prefer PPrune, you can find similar quotes over there.

Still just anonymous people (like here) who may or may not know what they are talking about.  You don't know they really are or what they know, or who wrote the All Aero bit.  I've searched numerous pics of Mark 5a's and can't find any with that crazy leading edge treatment and can't find any OFFICIAL accounts that describe it, so I will default to skepticism, and my own knowledge of how dangerous that kind of LE contamination is.   If  that kind of surface treatment, equivalent to a heavy coating or rime ice, improves aileron effectiveness, well, there's a whole new paradigm.

@JohnK I don't think it is increasing the aileron effectiveness, instead it increases the turbulence over the aileron close to stall. This gives an early indication of impeding stall, which is more friendly than the laminar flow suddenly stalling, especially in a training aircraft.

No that kind of roughness will simply cause a full separation and complete loss of aileron control at an angle prior to the normal stall AOA.  I could be wrong in all this, but I want to see an authoritative source because this is pretty bizarre, and like I said, all the pics of Provosts I can find all show normal clean LEs.

I understand and appreciate a healthy dose of skepticism! I was a bit skeptical in the beginning, but I found quite a few sources that I thrust now. If I find any images or something authoritative I'll keep you posted.

@JohnK One more source from Flightglobal added.

Good find!  I'm satisfied that the treatment was intended to modify stall behaviour and will delete my post.  I still think tho that it was just done experimentally and may have not worked so well because I still can't find a picture of one in service with that treatment.

I am a helicopter pilot (ex RN) but my original training was on aeroplanes (Bulldog at RAF Leeming 1979) prior to helicopters. The FTS at Leeming was operationg JP 3's & 5's.
My understanding of the rough leading edge on the outer part of the wing on the JP.5, I cannot remember if it was also on the JP.3, is that it was there to help keep airflow attached and give/maintain aileron control at lower speeds and therefpre high angles of attack (AoA) i.e. close to the stall. Ideally you want the inner part of a wing to stall first, as this will reduce the chance of wing drop and therefore the likelihood of a spin.
If the outer part of the wing stalls first, and a wing drops, the AoA on that wing increases as it drops increasing the stall, increasing the wing drop etc. As the aircraft rolls due to the wing drop, the other wing goes up and therefore the AoA reduces and the wing may be unstalled. This may assist the roll towards the down going wing increasing AoA on the wing and exacerbating the conditions of a spin.
Many aircraft have other ways of trying to achieve the effect of aileron control at slow speed/reduce wing drop:

Fixed (leading edge) slot - e.g. Douglas Dauntless and Grumman Avenger. Postioned on the outer leading edge, ahead of the ailerons. At higher AoA air passes through the slot re-energising and therefore re-attaching the airflow helping maintain aileron effectiveness. Helpful to have aileron control at low speed (particularly when deck landing).
(moveable/automatic) Slats - e.g. Messerschmitt 109, Fairey Swordfish. Positioned on the leading edge ahead of the ailerons. Some are spring loaded to open (pop out) and create a slot as the air pressure on the leading edge reduces as speed reduces. Reduction in speed means increase in AoA. The slats open to form a slot between slat & wing which helps re-energise and therefore re-attach the airflow ahead of the ailerons. Others open due to the relative change in pressure above and below the wing. Apparently in fighters, like the 109, not having the slats lockable can mean that they can "pop" when the AoA increases uneavenly during hard manouvering causing the wings to rock spoiling aim.
Some types Westland Lysander, and some modern light aircraft types, have moveable slats along the whole leading edge. This reduces take off and landing speeds and therefore stall speed. These may be selectable and opened and closed as required, like raising/lowering flaps.
The Fiesler Storch had a fixed slat, creating a slot, along the whole leading edge. The Storch has a very short take off/landing performance.
Washout - various types. Effectively the whole wing is twisted (leading edge downwards towards the tip) so that the angle of incidence and therefore AoA is less at the tip than at the root. Thus the wing should stall near the root first.

If any body reads this with proper aerodynamic knowledge and finds I have made some errors, created misconceptions, please correct, explain my errors.
IRW
7 Feb 2021
I recently found AP.3456, now called the "CFS Manual of Flying", online (https://www.gov.uk/government/publications/foi-responses-released-by-mod-week-commencing-13-january-2020) and downloaded it.
So far I can find no direct reference to the "rough leading edge" on the Jet Provost (Strikemaster). From what I have so far read in what I have downloaded, I am still of the belief that the "rough leading edge" is effectively a vortex generator (perhaps it could be called a boundary layer exciter/re-energiser.
I would recommend that anyone wanting more information download and look particularly at;
Vol.1 Principles of Flight, Chpt.6 Stalling, Para.8-10 (Tip Stalling) and Para.30-34 (Autorotation);
Vol.1, Chpt.10 Lift Augmentation, Para.3-12 (Slats) & Para.44 (Vortex Generators).
Since writing my original comments, I have spoken with a former RAF QFI who instructed on Jet Provost 3's & 5's and he is in broad agreement with what I wrote. He cannot remember however for certain if the 5's had the "rough" leading edges when he was flying them.
I hope that the link above and the references may be of interest and help answer the "rough leading edge" question.
IRW


text:
Did Boeing really use ferrets to run wires through aircraft during construction?
I've seen many articles on the internet (here, here & here) claiming that Boeing used a team of ferrets to run cables through hard to reach areas when building aeroplanes, but I've never seen any official sources to back these claims.
Is there any truth to this, or are they just baseless internet rumours?

Surely you jest @Sam, everyone knows the internet is the golden source of ultimate truth!

Using a cute rodent-like animal to do actually-useful work by running wires through tight spots in a jumbo aircraft is literally YouTube-viral material. They'd be crazy not to farm the upvotes, given the recent ongoing troubles /s

Imagine all of the interesting places service crews would find corrosion from rodent urine. Maybe a few extra wire bundles that always seem to lead to ferret skeletons.

One answer below mentions defects. To that one might add defecation. Somebody is clearly taking the p...

In my best Cliff Clavin voice:  Actually, the ferret isn't a rodent.  They are members of the weasel family, and they are predators that eat rodents.

https://www.ferret-school.co.uk/working-ferrets/video

No, Boeing didn't do that.
I asked their assembly plant tour
to confirm or deny this, when I found
a report that around 2010 some visitors heard this from a tour guide.  On 2020 Nov 3 they replied:

Hello,
Thank you for contacting us with your inquiry. This is a popular urban myth, there are no records or any other evidence that this was done at Boeing.
Thank you again for your interest.

Thank you, Camille, for taking the effort and contacting Boeing. Case closed.

Well, just keep in mind where the statement came from, and what is their recent track record on...

I don't trust my memory enough to actually answer, but this is triggering a faint recollection from an info board at the Boeing Museum of Flight in Seattle. Like maybe they tried this for a short time in the old Red Barn plant in the 1920s or 30s? The 1960s is way too recent, and I certainly wouldn't expect a current employee to know historical trivia like this. (If true...)

That's a clever idea...
No, they won't do that
Too many accidents, defect in an airplane is from tiny things like a wrong gasket, wrong pipe fitting, small crack that you'd have to take out a microscope to see. There are better tools and ways for doing that.
However, I can not say this isn't an idea somebody has tried, there are some reasonable truth to it... but definitely they won't use this method on the critical part of the airplane

I mean, it was in the 1960s. I could actually imagine this to be true.

@NoahKrasser Yes, the ferrets of the 60s where much more trainable than those reluctant and rebellious beasts of today.

Felicia was used as a pipecleaner in the National Accelerator Laboratory https://history.fnal.gov/felicia.html

I got a Not Found (404) error when I clicked on the link about Felicia the ferret.  Here's the archived copy of the page from archive.org.


text:
What are these protruding things on this Russian military aircraft (MiG-31BM)?

See the video
In the video it is clear that the jet takes off and lands with all these 3 things "open/stretching out" (so it seems to fly just like that - not retracting them).
Here is Wiki on that model.

Related: What is the purpose of the “Mirror-Thing” over the Mig-29 Cockpit?

The upper thing is a mirror for the WSO's (rear seater's) periscope.  It gives that position some forward visibility when extended.  Without it, I doubt that position could see the runway.  There are several other Russian aircraft with periscopes.
The lower ones are speedbrakes.
Looking at the underside of the vehicle my speculation is that they interfere with the landing gear retraction, so are extended until that point.  But if that's true, do they have to extend when the gear come down for landing?  No idea.  I can't think of another good reason for them to be open on takeoff.
A comment from ymb1 showed a very nice image of the doors/speedbrakes on wikimedia
This shows that they need to be extended until the gear is retracted.

But then why are the air brakes extended for takeoff? I did not watch the video, but the questions says takes off and lands with all these 3 things "open/stretching out".

Yes, or rather, the landing gear doors double as airbrakes. Because, why not? The extra drag at takeoff is insignificant for this aircraft.


text:
What were those multiple flights leaving London night of 29th Aug 2019?
First time post here, please let me know if more detail needed (and which tag would suit it best).
I live in Essex UK, in the evening normally see lights of planes on approach to the London airports.
This evening (29 August 2019) from 21:00 BST / 20:00 UTC I have seen lights of planes flying away from London in large numbers (at least 30 when I started paying attention).
They were in groups of about 5, then another group following not far behind. They appeared to be heading in an easterly direction away from London.
Could someone help to shed some light on this? Have lived in this area for 15 years and never seen anything like this.

Investors running away before Brexit?   ;-)

Welcome to Aviation.SE! Would you say it looked like they were heading out over the Channel? If they went in groups of about 5, do you have an estimate of the amount of time between one group and the next?

If anything, I'd say they were heading away from the channel. The group spacing was really tight - they seemed to be only a few seconds apart (although distance from myself to them may have affected that?)

Could you detail where you were, which direction you looked, which direction they went and whether you‘d estimate them higher or lower than the arrivals you normally see?

at this time of evening, usually see 3 to 7 lining up to come in to land (east to west), fly over my house and then split off, presumably to get to Stanstead/City airports). Tonight they were flying from opposite direction and in really large numbers.


text:
What is the material of snubber brakes?
What is the material of snubber brakes that is used for stopping the spin of the nose landing gear? KC-135, Boeing 747, 727 are the aircraft that I saw with these snubbers.

Actually brakes on NLG are optional, even for Boeing 747

This company provides brake components for the B737,
the snubber brakes being among them:
 (Source)
They are made of what they call "AFT 200" material, which is described as:

a phenolic treated, brass wire inserted cloth laminated under heat and pressure to a dense, strong composite. AFT 200 provides good fade and wear resistance and may be machined using standard, industry accepted practices. Its high strength makes it suitable for gear and lug driven applications.

I don't know if the snubber brakes in a KC-135 Stratotanker use this material as well, but the following picture shows where they would be installed:
 (Source)


text:
Why does the helicopter Robinson R22's rotor blade have flat part as in the picture? What is it for?

Picture source:

Picture source:
This is Robinson Helicopter R22's rotor's blade. What is this flat part for as indicated by the red line? What is the aerodynamic benefit of putting it? There are many symmetric airfoils but no flat part like that.

Are you sure about that? https://www.nasa.gov/image-feature/langley/100/naca-airfoils  Many seem "flat" in that area.

For example, lower-right, 5th from the bottom.

@Steve, I checked the NASA's link, I didn't see any such flat extension. Moreover, it will extend separation/delay the upper wind meet the lower wind. The very basic of wing is the cord line is as short as possible. To meet the required wing area then it made long so the ratio of its long to its cord will be as big as possible. It is the very basic, it is the most efficient wing.

The trailing edge part of an airfoil is the most "sensitive" part of it i.e. the part which changes the aerodynamic characteristics the most. That's why for example control surfaces like ailerons are  placed there.
Backward extension of the trailing edge are normally used to decrease drag for free basically without modifications of the lift. The following plot from this NASA report shows $C_l$ and $C_d$ for several "Static Extended Trailing Edge" configuration. The plots to be compared are the ones labelled with a circle (baseline NACA 0012) wrt the ones labelled with an x (10% chord flat extension):

It can be seen that extending the trailing edge backward brings a small reduction in $C_d$ and a slight increment in $C_l$.
This report nicely describes why that happen.
This report instead shows the (positive) impact of such a device for helicopter application.
I'm quite sure that also $C_m$ becomes more negative at high AoA but I couldn't find a plot to corroborate this claim.

Actually, a bit different, but I accepted. The test in that report is extension for a fix wing acts as flap while in the R22's case is as a rotating wing. But as mentioned in the report that the TE extension increases the cruise efficiency, so for the rotating wing we probably may assume that it is being cruising.

In the report also a flat (i.e. without downward bending) leading edge extension is considered (the plots with the x) and this is basically what we see on the R22. So those plots can be totally used to understand the effect of the extension on the R22, which is a slight reduction of drag and increase of lift at high AoA. I'm quite sure that that extension modifies the pitching moment as well (less negative), but I couldn't find a plot for that.

@sophit: But why not just use a longer airfoil? Shouldn't that be even less drag then elongating it?

@AirCraftLover: here I've found another nice article about the topic and applied to helicopters

@U_flow: well, the increase in $C_l$ is more or less a fake since this plate extension increment the lifting surface and lift is proportional to it. Drag decreases because (according to the literature) the plate keeps the upper and lower boundary layers separated longer and that decreases drag. The report I linked in my answer contains an explanation about that process and some pictures as well.

@sophit i see your argument, but that does not explain why the designer did not choose a simply longer airfoil from the start?

@U_flow: simplicity I suppose. Maybe during design phase Mr Robinson realized that he needed less drag and a bit more lift plus (as written by @JimHorn) a simple and sound solution by a structural point of view as well. This compromises/corrections happen quite often during design phase.

@U_flow Because there was no reason to.  If I can put winglets on an airliner wing, and by reducing span-wise circulation get the same amount of lift from from a shorter wing, then I would.  If it reduces the inner structure complexity of the wing, reducing weight and cost,  and makes the plane smaller around ground obstacles, then I'd do it.  Same here.  If I can produce the same L/D ratio with a thinner airfoil with less mass and cheaper manufacturing, then I'm doing it.  Why choose a larger airfoil if a smaller one produces the same performance?

@MaxR: very good point. Can I add it to the answer?

@sophit Of course!

I assume the thin aluminum skin of the rotor is bonded at the trailing edge to keep the top and bottom together there. Due to the forces involved, that feature allows a larger area of close contact, maximizing the strength of the bond. That would be a poor place for rivets and aluminum bonding is notoriously picky to prevent long term failure so having a robust joint is critical, especially in the high stresses of a rotor.


text:
What is the best design to stack wings of a triplane?
I would like to design an ultralight airplane, which probably the total mass will be around 400kg. The speed should not exceed 200km/h. Forget about what the engine I will use. I intend it can land and take off in a small road and/or in a common road, which the road line not more than 2.5m each direction. If I have to occupy both direction, mean the road width is just around 5m, plus small space beside the road in both side. Beside the road, normally many electrical poles. So, not many space available.
To tackle the situation, I need to change wings design without reduce the wing area (A in m2). Was discussed earlier here some of the triplanes that were used during the WWII. If they were used during the war, that mean that such design was safe enough. But, I have a bit confusion regarding how to place the wings' stack? Here are the three options design.

The wings stack are lean to the tail.
The wings are stacked exactly over another.
The wings are lean to the nose.

Another thing. We know that the closer wing to the ground will produce what is called earth deflection (CMIIW about the terminology) during take off. That will make the plane requires longer time to take off. In my opinion, the same effect will occur if we stack the wings too closed one to another, especially if the wings are stacked lean to the nose, the deflection will hit the lower trailing edge if there is no enough space. So what is the best design in this case? And what is the best space?

Ultralight at 400kg? In which country? In the US that would definitely not qualify as an ultralight, but I know other countries have different rules and definitions of "ultralight."

I am not sure actually what is the definition of ultralight and I don't know how aircraft is classified. 400kg would be included the pilot (I myself if 71-72kg, the engine probably will be 75kg). But forget about it. Just see the 400kg regardless of the class. I am just concern about the triplane wing, and what is the best configuration to make it fly savely.

The reason I ask is that in the US an ultralight aircraft cannot exceed 115kg empty weight, including engine, not including fuel. I don't know of any ultralight triplanes made in the US and designed to meet part 103 rules. Your design would probably have to be certified as experimental/amateur-built.

Definetely my plane is amateur, not intended for selling. My plane will more than 115kg as the engine itself already around 75kgs, a car engine. I am not in US. I am in Indonesia, that aviation rules in our country also I don't know. But I will find it once I can build my airplane, or at least after the calculation is fixed. This is just amateur, not commercial, or not even experimental.

But if I put a real airplane engine to my airplane with probably 50HP 25kg, probably I can redesign and recalculate so the weight will not exceed 115kg. But the most important thing now, what is the best choice from those 3 options?

Have you looked at any of the available bi-plane and tri-plane kits that currently exist?  http://aircraftproducts.wicksaircraft.com/category/aircraft-kits

The HoneyBee is pretty close, with 19 foot wingspan:  The H-2 Honey Bee is a strut-and cable-braced aerobatic biplane with four, equalspan, 8-foot wing panels... The prototype and early versions used engines in the 40-46 horsepower range, but the designer later moved up to an engine of 65 horsepower.  In 1992, an H-2A Honey Bee was named "Best" in the combined Ultralight/Lightplane category during the EAA East Coast Fly-In at Wilmington, Delaware. Wing Span is 19 Feet, Fuselage Length is 15 Feet, 9 Inches,

Also, in the US the speed of an ultralight is restricted to 55 knots/102 km/h.

Another collection of planes here  https://www.pilotmix.com/tag/aircraft-database/biplane  Kiebitz is only 118kg!  Have to browse their website to find dimensions.

http://www.kiebitzflieger.de/  7.6meter wingspan.  That will fit your road nicely.

Thank you all my friends. Your comments are very useful.

@jamesqf, thank you for the info. Thats quite interesting to know such many info have to be considered regarding aircraft.

@crossroads, I think I will make it from scratch, except the engine, of however. Even the propeller I will make myself.

Indonesia will let you design, build and fly your own airplane? I am impressed. :) Good luck!

@JuanJimenez, that possible as long as no town we pass. I am stay in a village, and sometimes I have to check my plantation which the distance around 600km from my home. I also need to check the plants from above to see if all the plants are grow properly, uniformly, healthy. Of course I can not fly it in a town, especially in the capital.

@AirCraftLover For this application I would recommend that you consider building a gyrocopter instead. Easier to design and build, lightweight, easier to land in a small area, and it will give you the kind of visibility that is more appropriate to check your plants from the air.

Dear @JuanJimenez, I was thinking that one too, so do trike, but I think both are not so reliable. I am so sure to the rotor of the gyro copter, I can not rely on it, so do with wing of the trike, the strength and less controllable. But also I realize, to monitor such plantation from above for short time fly, also considerable.

The rotor system on a gyro is much simpler than on a helicopter, and much more reliable. I used to work on military helos, and I've examined both. Gyros are infintely simpler to build, operate and maintain. They are also safer. If you run out of power with an airplane over your plantation, good luck. With a gyro you can land on almost any clearing. 600km is pushing it, but with a gyro you can land on a road in 20 meters and pull up to a gas station to fill it up. :)

Is that save enough to fly around 600km with gyro or trike? That very interesting if is. I have watched many of them before I came to a conclusion to build airplane.

Dear @JuanJimenez, which one is cheaper and easier to build a gyrocopter than a trike? In my mind, build trike is cheaper and easier.

You will not get the necessary range from a trike, IMO.

That what is in my mind. So, that one is drop from option.

Wing stagger was mostly chosen to improve pilot vision: In single-seaters, a positive stagger would allow to place the upper wing ahead of the pilot, improving the field of view.
Large bi- and triplanes had no stagger. Here the pilot sits ahead of the wing and large aircraft fly mostly straight, reducing the need for the pilot to observe the airspace around him.
However, if you look for a proven design of a very compact triplane, I would like to suggest the Italian Pensuti triplane. It had a wingspan of only 4 meters and a total weight of just 230 kg. Emilio Pensuti, a test pilot with Caproni during WW I, designed it as an easy to fly aircraft for the common man. Therefore, it is sometimes also called the Caproni-Pensuti triplane. The first version was powered by a 35 HP Anzani engine while a later development, the Breda-Pensuti 2, used a 80 HP engine.
Of course, its wings had no stagger.

Drawing of the Pensuti triplane (picture source). Yes, it did fly!

Pensuti triplane in flight (picture source)
If you build one, I would strongly suggest to change the wing airfoil to a thicker one with the same amount of camber.

Little worried about that one in a cross wind.  Might need a good set of ailerons.  Not bad in terms of symmetry though.  With wheels cross wind might actually roll in slightly windward, but push it sideways.

Thank you Peter Kampf. Very nice. There is one comment by @pilothead which referring the physic analysis regarding triplane as below. It is very nice. https://www.fullsizeplans.com/images/nffs/Lift%20EfficiencyBiplane.pdf

To answer your explicit question, I'll note that both the Sopwith Triplane and the Fokker Dr.I are arranged in the 'lean towards nose' style.
However!  The Wainfan FMX-4 Facetmobile might be of interest.

Wingspan: 15 ft (4.6 m)
Empty weight: 370 lb (168 kg)
Gross weight: 740 lb (336 kg)

I read about it. Very interesting. But seems it still beyond my knowledge. There are more researches to build such aircraft. But thank you anyway for the info so I have another insight and it open another option what to do.

While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference.  Link-only answers can become invalid if the linked page changes. - From Review

I've always wondered about the aerodynamics of the Facetmobile.  Seems like the sharp angles would create a lot of drag.  But something with the same body plan, but a smooth profile?

Dear @jklingler, can you please explain more? Is your suggestion you intend to me?

@AirCraftLover My comment is a reply to Roger's answer. IMHO the post doesn't really answer your question about the differences, benefits and consequences of the wing-designs. It would be better suited as a comment since it provides additional information that isn't totaly off-topic.

Do note that total wing area of a multiplane (biplane or triplane) wing configuration does not give the same performance as that same area with a monoplane. For a monoplane, all the wing deflects air downwards yielding lift. For a bi- or tri-plane, the wings all deflect the air together, reducing the effect of each. So a Cessna 152 with a 33 foot span would not fly if converted to a biplane with a 16.5 foot span or a triplane with an 11 foot span, to give an example.
Thus the concept of span loading. All fixed wing aircraft get their lift by deflecting air down as they pass. The amount of air they can deflect depends on their speed, their span and their weight. For minimum airspeed, the use of high lift devices is more effective than adding multiple wing planes. The main reason biplanes and triplanes were common in WW1 was for strength with the materials and understanding of aerodynamics at the time.
You might also note that many single place experimental aircraft designs have 5M spans already.

Actually, the real reason for triplanes was the desire to reduce span and with it roll damping. Dogfighting favors the fastest possible roll response. You are right about the limited understanding of aerodynamics, though. Caproni triplanes were really a folly.

Age old question of turning vs speed.  Triplanes were very difficult to deal with one on one in a turning situation, but were slower.  A very common theme in aviation history.  But these "follies" did have their moment, until continued progress changed designs once again.

@PeterKämpf I always thought that the good roll rate was an unintended bonus, and that the driving reasons for multiplanes were materials and misunderstanding airfoil interference. Could you elaborate on your comment? Why were Caproni triplanes a folly, or more so than, say, Fokker triplanes?

@Peter Kampf may have been talking about the 3x3 flying boat,  that one may have been a little off

@AEhere: Comments are not ideal for elaborate answers; better ask officially. Caproni started with biplanes, made the Forty-series triplanes to carry their weight but returned to biplanes with the Fifty-series. And Fokker only made the Dr I triplane after pilots encountering the Sopwith Triplane expressed their desire to have such a thing, too.

@PeterKämpf Thanks, I'll ask once I know what my question is :)

A good starting point would be the Curtiss JN-4 "Jenny" biplane.  Plenty of wing here, no need for triplane.  You want long wings for easy slow handling.  Warplanes designs generally are not as stable and do not make good recreational aircraft unless you are a very good pilot.
Stacking wings leaning towards nose reduces interference and maintains airflow over lower wing at higher Angle of Attack, making for a gentler stall.  This design is the fore runner of slats, which are also very effective.  You also want wings spaced as far apart as you can for better lift (get rid of the third wing).
It is surprising that there are not many recreational biplanes around these days, as they offer simple, rugged, reliably safe construction and lower flying speeds.
I would recommend continuing to research this, particularly to get a good engine/aircraft match.  Good luck!

But the OP states that he wants a short wingspan to enable landing on roads.

Landing on narrow roads is more a function of landing gear width.  You need to be under control.  Very concerned that these "brilliant" triplanes aren't around very much these days.  Pilot will probably get killed "landing on road with many electrical poles".  Simply not a good idea.

@robert-digiovanni, I understand that very hard to land it in a very narrow road. That my main concern how to make it can land safely. In order to "guarantee" it, I have to do some modification to the airplane so can fly with very slow speed, probably in just 20 mph. I have studied some eagles and birds how the expand their wing during "landing". Have a lot of study to be done here.

Another advantage by applying bird's wing principle, it can land very short. Not sure whether can take also very short as there is distinctive different between how aircraft fly and how bird fly, especially the catapult generated by the legs power.

This is why you want forward "lean", also called stagger.  This, like slat, will help lower landing speed!  Also, lower aspect ratio wings (shorter and wider) with undercamber will give you the lowest landing speed.  The longer, thinner "albatross" wing, though more efficient (better gas milage), stalls at a higher speed.  You don't need triplane to do this.  I would recommend balsa models to get lowest speed for a given weight, and a large field to practice landing on your first flights.

Plane in picture does not have forward lean, but flew 250 feet from a highway overpass (around 22 feet drop).

@Robert DiGiovanni: I disagree.  Landing on narrow roads, as the OP explains it, is about not hitting telephone poles, fence posts, or roadside brush with the wing tips.  (I think we both agree that landing on such roads is not the wisest possible course of action :-))  But if you have adequate wingtip clearance, just about any SEL plane has suitable gear width.  I've certainly landed on a number of dirt strips with wheel tracks no wider than a typical rural road.

Just a little worried about wing interference in the small triplane when the relative wind shifts.  Notice, in a cross wind without the stagger, there would be a lot of turbulence around the lower wings in a slip.  I do not think the Pensuti made it to mass production.  The Curtiss JN-4 biplane has a wingspan of around 44 feet.  That is less than 15 meters.  I think I'd rather find another place to land if it was that tight.

Dear @RobertDiGiovanni, there is one explanation that is very good regarding monoplane, biplane, and triplane. You may find it here. There are quite detail and reasonable explanation regarding the wing's gap and the stagger.

Again, I have to thank to @pilothead as his info has helped a lot. Thats all requirement we need. Gaps, stagger, and and the wings area requirement are comprehensively compared to monoplane.

@RobertDiGiovanni, unfortunately is not easy to find landing space in my place. This airplane I will use from my home to my plantation. In the plantation itself still possible, but not at my home are.

Excellent paper on biplane and triplane efficiency, thanks!


text:
What to be considered in designing airplane tail (vertical and horizontal stabilizer, elevators and rudder)?
I would like to make a small amateur triplane with it maximum weight approximately 400 kgs with maximum speed 100 knots (180 kph). I have read many discussions about how to calculate the wing requirement in relation to the weight, the speed, the wing shape, the airfoil shape, and so on. Unfortunately not so many discussion I found here about tail part.
What is the aspect to be considered in order to have the right design? Tail parts I meant here are: vertical and horizontal stabilizers, elevators and rudder, including the airfoil shape and the area. This question is about low speed airplane only, not sonic and moreover the supersonic one.

The measurement of overall tail authority for stability and control (a function of tail surface area and its leverage or arm) is called Tail Volume and the link goes to a handy calculator page for working it out.

Thank you John for the nice link.


text:
What is an example of a quantitative analysis for the lift using Newtonian mechanics?
There are several different ways of explaining how an airplane generates lift. The simpler qualitative explanation uses Newtonian mechanics (the third law is invoked to explain how the wing pushes air down and is in turn pushed up by the air) whereas the more quantitative explanation uses aerodynamics and fluid mechanics.
I have been looking to find a simple model of an airplane wing that uses Newtonian mechanics to come to an approximate quantitative description of airplane flight. Everything I have found so far (such as this article) is merely qualitative.

There was an article in the EAA Sport Aviation magazine many years ago where the author was explaining lift pretty much like your article in your link, and he calculated the tonnage of air that has to be displaced at x feet per second per second to create enough force to hold a 747 up, and it was a lot, basically a package extending a chord or more below and several chords above that had to be displaced.  Trying to find it.

If you understand french, I recommend this article/video. In short, math shows all valid explanations are equivalent.

This article on the subject, one of the first discussing the issue, may be of help:          https://booksc.xyz/book/45382205/a4710b

@xxavier Good reference. The result from eqn (1), however, is from Lifting Line Theory. Using that, it was able to deduce a relationship between flow turning angle and AOA.

The governing equations of fluid mechanics, Navier-Stokes equations, are derived based on Newtonian mechanics (plus thermodynamics). The circulation theory of lift is derived using a simplified form of N-S equations. It's powerful because it's predictive for important things like lift and induced drag. The Newtonian explanation is not that useful because it's not predictive. Good for party talks, but poor for engineering.
That being said, if you couple it with the concept of control volume and mass conservation, you can derive something. Take a look at NASA Memo 1-16-59L. To summarize, as air moves past the wing, it gets deflected, so the lift in the vertical direction (normal to the incoming flow direction) is:
$$L=\dot{m}\Delta V$$
where $\Delta V$ is the portion of air that was induced across the wing interface in the vertical direction, $\dot{m}$ is the total mass flow rate of air through the wing. That's the Newtonian part of the story.
Now from the conservation of mass, what comes in = what goes out. So we can express mass flow rate as, assuming the wing is like a giant circle with diameter equal to its span (note that this assumption is the major pitfall of this analysis, since there is no reason the stream-tube has to be the diameter of the wing):
$$\dot{m}=\rho A_iV_{i}=\rho\pi(\frac{b}{2})^2V_{\infty}$$
where $b$ is the wing span, $V_{\infty}$ is the freestream airspeed, $\rho$ is air density.
As for the change in vertical airspeed, we can parametrize it by assuming the whole stream tube gets deflected by the wing through an angle $\epsilon$. Therefore, $\Delta V=V_{\infty}\sin \epsilon$, and:
$$L=\frac{\pi}{4}b^2\rho V_{\infty}^2 \sin \epsilon$$
That's pretty close to the lift equation that we know. In fact, if you express drag as the loss of horizontal airspeed, apply small angle approximation to the second order, then normalize the lift and drag by $\frac{1}{2}\rho V^2 S_{ref}$, you get (with $S_{ref}$ being the reference wing area, $A$ being the aspect ratio):
$$C_{D}=\frac{C_L^2}{\pi A}$$
That's the induced drag expression for an elliptical lift distribution that we would get from the circulation theory of lift. But that's pretty much as far as you can go. You have no way of estimating $\epsilon$ from first principle, so the theory isn't all that predictive.

Thank you for the answer and resource recommendation. You have said that there is no way of estimating $\epsilon$ from first principles, but could we not assume it is the same as the angle of attack of the wing, in effect assuming that the downwash is parallel to the slope of the wing?

@Pancake_Senpai We cannot. Assuming that gives you incorrect results.


text:
Do commercial passenger airplanes have cambered airfoils?
It seems to me that they logically would, since they have no need to fly upside down like an aerobatic plane would (so they would not need a symmetric airfoil for any conceivable reason). That being said, is that correct, and does anyone have a link to a reliable source where that is stated?

Look at pictures of wings.

I think it's safe to say that all passenger planes use cambered airfoils, although I wouldn't be surprised if someone finds a case of an aerobatic plane being used to carry a paying passenger, just to prove me wrong.
There's a fairly comprehensive list here. You'd have to look them up to be sure, but many of them use codes that indicate thickness and camber. For example, the first digit of a NACA airfoil is the camber.


text:
To what degree is CHAYKA radio navigation publically available?
With most of the Loran-C network in Europe shut off in Europe since 2015, public positioning services seems limited to satellite navigation (GPS/GLONASS/Galileo).
However, to what degree is the equivalent CHAYKA hyperbolic navigation network still usable? I'm having trouble finding information more recent than a decade old, making it possible that the system is no longer available.

You might find more information if your search for its Russian name, Чайка, with your favorite search engine. Looks like it actually means "seagull" so you might get more hits than desired.

I have attempted that, but have not been able to find a conclusive answer with my limited Russian.

I'll try but my Russian is also very limited.

Doesn't appear to be much information after 2010, but I'll keep on looking, it's kinda interesting and I can exercise my pidgin Russian.

The masts at Dudinka and Taymylyr (demolished in 2009) were 460 metres high.  this gives a clue that it may have been dismantled a while back.

@Raffles Yes, the Wikipedia page is up to date to that point, as the GRI 5960 chain is clearly no more.

I just stumbled upon  this link if you're willing to go through your favorite translator :D Even then they mention 2004 - 2007.

They seem to talk about GLONASS, so maybe the CHAKYA system is defunct.


text:
Do any aircraft carry boats?
A small boat could be part of general cargo, but that would typically just mean it's unloaded at an airport and transported to the nearest body of water by land infrastructure. This is not what I'm looking for.
Instead, is there any aircraft that can directly deploy a boat to (or retrieve one from) water?
I would imagine there are cases when moving a boat by plane could be useful, especially when there's little or no infrastructure available on land.
Does such an aircraft exist?

This answer includes a picture of a dingy attached to a wing of a PBY Catalina

You may precise what kind of boat (almost every seaplane may carry an inflatable safety dinghy).

There’s a super cool picture of a boat mounted under a wing bottom first and a question about its aerodynamics in the site. Can’t search now

@Antzi I found a question titled "Why was the boat mounted this way on the underside of the wing on the “Landseaire” flying yacht?"

on jet liners, the emergency evacuation inflatable slides are designed to float and be used as lifeboats. Does that count?

@Nelson that one:)

What about if the aircraft is a boat? For example, the Boeing 314 Clipper.

I have at home, a photo of a Norwegian (?)  P3 Orion which regularly (always?) carries an inflatable type lifeboat, in its bomb-bay, that can be dropped where needed.

I guess the inflatable slide doesn't count on modern airliners?

Yes. During and after WW2 several aircraft were converted to serve as "Dumbo" aircraft, dropping boats or rafts near people in distress. Other models were used as well, but the B-17 were among the most prominent. Most were retired when the helicopter gradually took over rescue operations.

Put one of these on an aircraft carrier! Then you'd have a boat on a plane on a boat!

And put a little model plane on that boat, so you'd have a plane on a boat on a plane on a boat.

And paint a small ⛵ on the model plane, so there's a boat on a plane on a boat on a plane on a boat...

It is quite common for float planes to carry canoes & kayaks, e.g.

I would like to suggest the "Landseaire" flying yacht which carried boats under the wings as per this question.

Why is the boat backwards?

@CamilleGoudeseune - follow the link to the other thread. Your question is exactly what that thread was about.

Wow, what a spirited and multifarious debate!

@CamilleGoudeseune Some of ‘em can get pretty rowdy around here!

It was one of the main roles for the Vickers Warwick in WWII.
From Wikipedia:

From 1943, Warwicks were loaded with the 1,700 lb (770 kg) Mk IA airborne lifeboat and used for air-sea rescue. The lifeboat, designed by yachtsman Uffa Fox, laden with supplies and powered by two 4 hp (3.0 kW) motors, was aimed with a bombsight near to ditched air crew and dropped by parachute into the sea from an altitude of about 700 ft (210 m).[36] Warwicks were credited with rescuing crews from Halifaxes, Lancasters, Wellingtons and B-17 Flying Fortress, and during Operation Market Garden, from Hamilcar gliders, all of which ditched in the English Channel or North Sea.[37]

More on airborne lifeboats...(also source for image above)
Of course, many WWII bombers carried inflatable dinghies, but I think the answer is looking for something more substantial.

The Fernic T-9 of 1929 was prepared for an Atlantic crossing and as a precaution had removable upper engine nacelles which could double as a life raft, including an outboard engine.

A less planned use of an airplane part as a boat occurred when in 1932 the Junkers W-33 of Hans Bertram and Adolf Klausmann crashed in a remote part of Western Australia. They removed one of the floats and made it into a boat for fishing and excursions.

If they'd only thought to make the whole engine removable for use as a boat, complete with a water prop to swap out for the air prop, the self-rescue would have gone much faster! :)

Took me a while to find this photo, from my personal archive from the East Fortune Airshow 2015  of a Royal Norwegian Airforce Lockheed Orion.
As I recall, the commentator stated that the orange object visible in the 'bomb bay' is an air-droppable lifeboat, for their search-and-rescue missions.

That seems too small to be a lifeboat.

@Nav It's likely an inflatable.  What you see is the drop housing to keep the boat intact while falling out of the sky and on initial impact.  Then once in the water it is deployed either by some manually activated mechanism (like opening a valve on a compressed air can) or automatically activated (some chemical reaction with water initiating) inflation mechanism.

Though at approx 10 ft long and 2 or 3 feet wide, it might just be a small life boat with a parachute package. (Dimensions estimated from the C-130 Fuselage being 10 to 12 ft wide (internal cargo bay width is at 123 inches https://www.af.mil/About-Us/Fact-Sheets/Display/Article/1555054/c-130-hercules/)

Allegedly, the length of one of those wingtips is 7ft7in or 2.31m (seperate sources) and that looks comparable to the length of that object, which would be adequate for a one- or two-man emergency liferaft.

While I wouldn't say it's impossible, the requirements of an airdropped lifeboat might not allow for such a small size: https://en.wikipedia.org/wiki/Airborne_lifeboat. This old patent shows more details of the mechanisms such a lifeboat needs: https://patents.google.com/patent/US2686323. It's also possible that the commentator who said it's a lifeboat, may have made a mistake. It resembles a survival kit though: https://lifesupportintl.com/products/sur-0300-00

Have a look at  https://www.irvingq.com/irvingq-products-services/aerial-delivery-search-and-rescue-products/aerial-delivery-equipment-sar-copy-2/skad-survival-kit-air-droppable/   and see what you think?

True. It's a life-raft (but not a life-boat :-) ): http://www.safeeurope.co.uk/media/7889/j-christine-belmonte_uni-pac-mission-versatility.pdf

A raft is, by definition, a kind of boat...

"Once the container touches the water, the second life raft is expelled and inflated automatically" "Survivor Capacity: 12 Person"

The Boeing C-17 Globemaster III can deploy boats. There are some videos on YouTube (example) that show the process:


text:
Why don't TAWS systems provide automatic avoidance?
After watching several episodes of "Air Disasters" where the pilots' response to a TAWS (terrain awareness and warning system) alert was, "huh, that can’t be right", and then they fly into the terrain. I am left wondering why don't these systems actively avoid the terrain (pull up) automatically?

I would have to disagree with most of what John K has said. I will try to provide my own answer as well.

Theoretically possible, but it would have to be a very expensive and complex sort of system, because it would have to manage pitch and thrust together, meaning it would have to integrate an autothrottle function in addition to an autopilot function

Current generation fly-by-wire aircraft have massive amounts of computing power and are capable of linking together autothrottle and autopilot actions already. Yes, it's expensive, but modern airliners are.

the risk level of that sort of incident, which are pretty rare outliers really when you think of millions of hours flown each year, doesn't justify the development costs.

Indeed, thankfully, all accident types are enormously rare in modern aviation. However, that doesn't mean we stop trying to improve and CFIT (controlled flight into terrain) accidents are actually some of the more common and certainly warrant the development of safer systems.
My answer: As ymb1 has shown, this system does exist already. Why is it not on airliners yet? Well, I think it will be soon. But there might be a number of issues.
Firstly: false positives, where a terrain avoidance command is issued without need. Say, for example, an aircraft is coming into land and passes over a tall tree, this sets off the system needlessly and could very well cause further issues with traffic avoidance and airspace incursions - pilots would be hesitant about allowing such a system.
Secondly, aircraft performance. For the jet fighter in ymb1's video the aircraft performance, it's agility and power, and the pilot protection (e.g., helmet and 5-point harnesses) mean that this type of rapid terrain avoidance command is possible and effective. For any large commercial airliner, those sort of commands are not possible (much lower thrust-to-weight ratios etc.) and so the aircraft would have to respond to a terrain avoidance command a long way out - this would increase the likelihood and issues associated with my first point. Additionally, things are not as secure in an airliner and so there is the very real possibility of hurting people and breaking things when such a command is followed - if this is a do-or-die situation, then who cares! But what if it's a false positive and now you've just injured 50 people for no reason.
I'm sure there are other reasons. But having said all that aircraft designer are looking for solutions for CFIT accidents. Currently, for airliners, the main solution seems to be greater awareness for the pilots. So, using HUD/HGS (Heads up display/ guidance system). Some even now have special cameras at the front so that the surrounding terrain is overlayed on the HUD for use in low-light, low-visibility conditions. I guess that is the current solution for now. So expect to see greater use of HUD systems with terrain overlays in airliner cockpits.

Theoretically possible, but it would have to be a very expensive and complex sort of system, because it would have to manage pitch and thrust together, meaning it would have to integrate an autothrottle function in addition to an autopilot function capable of abnormally radical zoom climb maneuvers and then recovering from the maneuver at the appropriate time.
So, theoretically possible, but it will cost eleventy jillion dollars to certify, and the risk level of that sort of incident, which are pretty rare outliers really when you think of millions of hours flown each year, doesn't justify the development costs.
However, in future as the world moves toward single pilot airliners (inevitable as the crew shortage is not likely to get better any time soon with collapsing birth rates)  and software and AI makes more and more things possible cheaply, that kind of automation of escape systems like terrain avoidance and windshear escape will probably come to pass.

It really doesn't :) The windshear escape already does that.

@ymb1 that's worth an answer